The present invention relates to the field of fibrous granules or agglomerates used as absorbents.
Small particulate-like or agglomerate absorbents have long been used for absorbing liquids particularly water and/or oils. However, the nature of the specific absorbents designed and used for particular end uses has changed significantly over time. Depending on the particular end use requirements and available materials, absorbents in use today are quite different in regard to their composition, physical properties and/or chemistry. Typical large volume end uses for particulate-like absorbents include animal bedding, cat liter, oil absorbents, water absorbents or absorbents used to remove oil from water surfaces. For example, with animal bedding absorbents it has been described as important that the absorbent material be non-toxic, have antibacterial properties and have high absorption capacity for urine and the like. With cat liter, some of the same considerations are present as with animal bedding, however, there is also a need for more rapid absorption and the ability of the material to clump or hold together when wetted becomes important. With oil absorbent materials generally the absolute oil absorbing capacity has been considered important in the prior art, as well as the density and integrity of the material. For absorbing oil from a (e.g., factory) floor generally a more dense, coherent material is required so as to avoid airborne dust, which causes difficulties with people and machinery, ease of removal and safety concerns. For absorbing oil from the surface of water, it is generally considered necessary that the absorbents be both coherent when wet and less dense than water, both before and after the material absorbs oil and/or water.
For example, U.S. Pat. No. 2,649,759 describes that for animal bedding typical common absorbents used are organic-type materials such as straw, peat moss, wood shavings as well as diatomaceous earth. This patent proposed use of a specific clay which is alleged as superior in view of its high absorbency, anti-bacterial properties, non-dusting properties and the fact that it is non-toxic.
U.S. Pat. No. 3,617,564 proposes an absorbent of low density corn cob granules which are formed of the cob with the center core removed. These granules are stated as having suitable properties, without any further treatment, for removing oil from fresh or salt water. Hydrophilic organic fibers have also been described as acceptable oil and/or water absorbents without a resin treatment. U.S. Pat. Nos. 4,829,045 and 4,409,925 propose adding calcium sulfate and Plaster of Paris, respectively to augment the properties of organic hydrophilic fibers. In U.S. Pat. No. 4,829,045 the natural fibers are peat fibers, which are pelletized. Calcium sulfate is added to act as a binding agent and a fire retardant. In U.S. Pat. No. 4,409,925 ground waste paper is dry mixed with Plaster of Paris and then agglomerated by the addition of water droplets. The size and density of the particles formed depend on the size of the water droplets. The resulting material is described as an oil and water absorbent and as performing superior to a clay product. The Plaster of Paris, although described as used in the prior art as an oil absorbent by itself, is used in this patent primarily for sanitizing purposes and is reported as actually reducing the oil and water absorption properties of the fibrous agglomerate material.
Resins are often used to modify the surface properties of organic fibers or particles to allegedly make the fibers or particulates better oil absorbents. For example, U.S. Pat. No. 2,692,861 describes an oil absorbent material for use as a floor sweeping composition. It describes conventional materials as sawdust, clays and sand. In order to improve the properties of these conventional materials the patent proposes coating the materials with resins which are "substantially free of paraffinic hydrocarbons". U.S. Pat. No. 5,308,497 proposes using a phenolic resin for treating fibers to make oil absorbent sheet materials, e.g., sheets of woven or nonwoven treated fibers. U.S. Pat. Nos. 4,519,918 and 4,537,877 use reject paper pulp fibers that are treated with specific resins to make them hydrophobic followed by dewatering, shredding and drying to form general purpose oil-absorbent materials.
The recognition that fibrous cellulosic organic fibers can function as oil and/or water absorbents has led to the use of fibrous waste sludge or white water waste solids as a raw material for forming a variety of absorbent products. This material represents an environmental and disposal problem for paper making companies and is a byproduct of primary pulping operations, recycle streams or waste paper pulping and the like. Generally, waste sludge or white water is a dilute stream of fibers unsuitable for paper making. The fibers may be too large or too small. Waste sludge can also include significant amounts of inorganic fillers (particularly if the sludge comes from a waste paper pulping operation). U.S. Pat. No. 3,876,497 describes a method of disposing of waste paper sludge by oxidation. U.S. Pat. Nos. 5,478,441, 5,332,474 and 5,423,993 describe methods of recovering the small or fibers for use in paper making. U.S. Pat. No. 5,240,565 converts the waste sludge into energy and charcoal. U.S. Pat. No. 5,346,549 forms waste sludge solids into a building material (e.g., concrete filler) by mixing it with coal ash.
Waste paper sludge is described as a preferred feed material in U.S. Pat. Nos. 4,670,156; 4,975,108; 4,753,917 and 3,770,575 which patents describe methods for making hydrophobic cellulosic fibers by rapidly drying waste paper sludge, pulp or some other fibrous materials. U.S. Pat. No. 3,770,575 states that the fibers need to be treated with a sizing agent, e.g., stearic acid anhydride, if the treated fibers are to be used to absorb oil from the surface of water. However, U.S. Pat. Nos. 4,670,156 and 4,753,917 do not require the use of a sizing agent. The pulp used in both of these patents was sulfite reject fibers which were exemplified as being made hydrophobic by high temperature flash drying alone. In U.S. Pat. No. 4,975,108 flash dried reject pulp fibers were mixed with a water soluble material, e.g., fertilizer, forming a controlled release material for use in soil.
U.S. Pat. Nos. 4,374,794 and 4,356,060 also describe treating a waste paper sludge. In the 4,374,794 patent, the sludge is dewatered, extruded into pellets and dried at temperatures ranging from 100.degree. C. to 150.degree. C. to form an oil and water absorbent material. U.S. Pat. No. 4,356,060 dries paper making waste sludge at a temperature of about 350.degree. F. after which it is sent to a hammermill where it is disintegrated into a soft, fluffy material which is used as an insulation product. For fire retardency purposes the material preferably contains at least 30 percent clay.
The use of cellulose waste sludge for forming a kitty liter product is proposed in U.S. Pat. Nos. 4,341,180 and 5,215,041. In U.S. Pat. No. 4,341,180 waste sludge fibers are dewatered, chopped into small pieces, mixed with sodium bicarbonate and then pelletized in a conventional pelletizer. A fluidized bed drier is used to dry the formed pellets. U.S. Pat. No. 4,215,041 mixes pulverized dried waste sludge fibers with 30 to 34 percent lime or gypsum, and then adds water to form a slurry. The wet slurry is then granulated in a circular drum followed by sizing, dusting with a mineral powder and drying in a rotating drum. The resulted particles formed are allegedly hard granules suitable for use as a cat liter.
U.S. Pat. Nos. 4,931,139; 4,560,527 and 4,621,011 describe surface conditioning of agglomerates or granular particles formed with organic fibrous material, preferably waste paper sludge fibers. This surface treatment is exemplified as accomplished in a rotating drum, preferably with added water to cause any upstanding fibers to be folded back into the fibrous agglomerates, or otherwise formed granular particles. In U.S. Pat. Nos. 4,621,011 and 4,560,527 dry waste or recycle paper is first fiberized by a size reduction device, such as a hammermill then further treated. However, this size reduction step is stated as unnecessary and problematic when wet cellulosic fibers are used, such as from waste paper sludge, as the hammermills plug up when the moisture content of the cellulosic material is above 20 weight percent. Moist fibers, regardless of whether they were first subject to a size reduction step or not, are then agglomerated in a horizontal rotating drum which also serves to "compact" the skins of the fiber agglomerates. Further, compaction can occur in a secondary rotating drum or fluidized bed drier. The resulting material is described as particularly well-suited for use as a kitty litter material. U.S. Pat. No. 4,931,139 is directed at a method of providing an oil absorbent material which addresses perceived problems with prior art processes which required pelletization and/or high amounts of inorganic fillers. These prior art fibrous particles were allegedly too dense, had dusting problems and/or "were fuzzy". The absorbent material in this patent was formed by flocculating waste paper sludge fibers into a mat or sheet which was then shredded and conditioned in a water mist (the shredded particles were tumbled in the presence of water to fold in the fuzzy outer fiber ends). The resulting product was described as a low density material which had a good absorption capacity for oil.
U.S. Pat. Nos. 4,721,059 and 4,734,393 also describe an oil absorbent material formed with waste paper sludge fibers. The sludge fibers are dewatered and then shredded to a fine particle size, less than 10 mm, followed by standard pelletization and drying in a rotary drum drier. The resulting materials allegedly showed good absorbency for oil.